Devices for capturing three-dimensional objects, in particular 3-D laser scanners, can be used for the detection of body contours.
Such laser scanners are used, for example, for three-dimensional contour detection for games consoles. Players can hereby operate the software of console games with their own body movements. For this purpose, a depth sensor is used in addition to a 3D microphone, a camera and the software.
The depth sensor is composed of a separate transmitter unit and a separate receiver unit. The transmitter unit consists of a projector generating a dot pattern. In this case, the dot pattern is projected onto a person located in front of the projector using a laser diode and a diffractive optical element (DOE). This dot pattern is read by the receiving unit—a camera—and converted by a processor into spatial information (3D-information). The number of generated dots plays an important role in the degree of detail and the quality of the spatial information.
To meet the demands for a more precise spatial image capture, the number of projected dots can be increased. However, a higher image quality of the dot pattern is required for this purpose than can be achieved with conventional diffraction gratings.
One possibility for generating dot patterns with a high image quality is the use of so-called “Micro Electro Mechanical Systems” (MEMS). These MEMS have a mirror that oscillates very fast about two axes and continuously deflects a laser beam, thereby generating a dot pattern depending on the position of the mirror.
To capture a detailed three-dimensional object with high precision, the dot pattern requires, on the one hand, a sufficiently large number of projected pixels and, on the other hand, a high image quality of the projected pixels.
Although the image quality and number of pixels can be increased by using MEMS, such devices, however, require relatively complex spatial arrangements, resulting in a large number of components. The resulting small tolerances make mass production expensive and thus unprofitable. Additional adjustment steps (active and passive) to compensate for tolerances add complexity.
A conventional device for capturing a three-dimensional object using a rotatable mirror (MEMS) is shown schematically in FIGS. 1 and 2.
The device includes a diode laser 110 and a collimator lens 111. The light emitted by the diode laser 110 which is then collimated is incident on a polarizing beam splitter 112. The radiation 113 reflected by the polarizing beam splitter 112 is incident on a deflection mirror 115 where it is redirected to the MEMS 114. The MEMS 114 oscillates continuously about two axes over a predetermined angular range, thus generating with the deflections (at a predefined distance) a (divergent) dot pattern on an object. Since the interior of the components of the optical system must be free from dirt particles, for example, because MEMS joints can attract dust due to static electricity and thus become inoperative, all illustrated components are sealed to the outside by a housing (not shown here). The sequentially generated divergent dot pattern 117 is coupled through an optically transparent protective glass 116.
After the dot pattern 117 is emitted, it is (partially) reflected on an object and the radiation 119 reflected on the object passes again through the protective glass 116 and enters the device (FIG. 2). The reflected light 119 propagates through the MEMS 114, the deflecting mirror 115, then passes through the polarizing beam splitter 112 and is focused by the focusing lens 126 on the detector 124. The signal received by the detector 124 may subsequently be converted into spatial information about the (partially) reflecting object.
Disadvantageously, assembly is very expensive due to the large number of required components. The spatial arrangement of these components also requires larger components due to their structure. However, these prevent a desired small size of the device.